In a vehicle such as a truck having a body with a frame structure, an axle structure of a driving wheel of a full-floating type bearing has been widely adopted. In recent driving wheel supporting structure, a unit structure of a double row rolling bearing has been widely adopted. This unit improves the readiness of assembly and reduction of weight and size. One example of such a prior art vehicle wheel bearing apparatus is shown in FIG. 9.
In this vehicle wheel bearing apparatus, a drive shaft 52, connected to a differential apparatus (not shown), is inserted into an axle housing 51. A double row conical roller bearing 53 is mounted on the axle housing 51. A wheel hub 54 is rotatably supported by the double row conical roller bearing 53. The wheel hub 54 is connected to a flange 56 via hub bolts 55. A pair of inner rings 57 is connected to each other by a connecting ring 58. The rings 57 are fit onto the end of the axle housing 51 and then securely fastened by a fastening nut 59. An outer ring 60 of the double row conical roller bearing is fitted into the wheel hub 54. The outer ring 60 is axially secured by both its ends being sandwiched by the flange 56 of the drive shaft 52 and a brake rotor 61. Double row conical rollers 62 are rollably contained by cages 63 between the annular space between the inner and outer rings 57 and 60. Seals 64 are arranged at both ends of the annular space to seal off the inside of the wheel bearing from the outside.
The inboard side end of the inner ring 57 is formed with an annular stepped portion 65. The stepped portion 65 receives and mounts a seal ring 66. An annular recess 67 is formed on the outer circumferential surfaces of the inner rings 57 at mutually abutted portions of the pair of inner rings 57. An elastic seal ring 68 is fit into the recess 67. These seal rings 66 and 68 prevent penetration or ingress of rain water or dusts into the axle housing 51, leakage of differential gear oil to the outside and ingress of the differential gear oil into the inside of the bearing (see Japanese Laid-open Patent publication No. 99172/2001).
However since the prior art vehicle wheel bearing apparatus has a structure where the double row of conical roller bearing 53 is arranged between the wheel hub 54 and the axle housing 51, the driving shaft 52 is inserted into the axle housing 51 and the flange 56 of this drive shaft 52 is connected to the wheel hub 54 by the hub bolts 55, a reduction of the weight and size of the bearing apparatus is limited. Also, the assembly of the bearing apparatus is complicated due to the requirement of a large number of structural parts.